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Metallic Hydrogen Produced in the Laboratory at Static Megabar Pressures

April 19, 2016

Metallic hydrogen has been produced in the laboratory in a diamond anvil cell at pressures in the 1.2 to 1.7 megabar regime and at high temperatures.

Prof. Isaac Silvera and his student Mohamed Zaghoo and postdoc Ashkan Salamat pressurized hydrogen and then heated it with a pulsed laser in an innovative geometry, producing thin films of liquid metallic hydrogen (MH). The challenge of producing metallic hydrogen was set forth over 80 years ago by Wigner and Huntington who predicted that when hydrogen was compressed to high density at low temperature, the molecules would dissociate to an atomic lattice that is metallic; the required pressure for this transition is now estimated to be over 4.5 million atmospheres, a pressure that has never been achieved on hydrogen, as the diamond anvils fail. The researchers used another pathway to the metallic phase. At achievable pressures of a few megabars, solid molecular hydrogen is heated to melt to liquid molecular hydrogen; at still higher temperatures the molecules in the liquid are predicted to dissociate into liquid MH as a first-order phase transition. When this phase line is crossed the reflectance and transmittance are observed to abruptly change to that of a metal, with evidence of the first-order transition from latent heat of transformation. Efforts are underway to produce MH at lower temperatures where it may be a room temperature superconductor.